New evidence appears to back the idea that the Roosevelt administration helped cover up Soviet guilt for the 1940 Katyn massacre of Polish soldiers.

In an exclusive story, the Associated Press says that newly released documents support the suspicion that the US did not want to anger its wartime ally, Joseph Stalin.

The documents were made public by the US National Archives on Monday.

More than 22,000 Poles were killed by the Soviets on Stalin's orders.

Soviet Russia only admitted to the atrocity in 1990 after blaming the Nazis for five decades.

The documents show that Americans prisoners of war sent coded messages to Washington in 1943 to say they had seen corpses in an advanced state of decay in the Katyn forest near Smolensk in western Russia.

The group of American and British POWs had been taken by the Nazis against their will to witness the scene.